A new NBS/oxone promoted one pot cascade synthesis of 2-aminobenzimidazoles/2-aminobenzoxazoles: a facile approach

A new strategy for the synthesis of 2-aminobenzimidazoles via a reaction of alpha-halogenated cyclohexanone with guanidine is reported. It provides a facile N-bromosuccinimide (NBS) mediated transition metal free, sustainable path for the synthesis of 2-substituted azoles. NBS along with the oxone promotes in situ halogenation of cyclohexanone, which in turn, when allowed to react with guanidine, afforded 2-aminobenzimidazoles (2-ABI). This eco-friendly protocol provides a competent laboratory synthesis method associated with significant advantages such as greater selectivity, cost-efficiency, mild reaction conditions, absence of chromatographic purification, clean reaction profile, and a simple work-up procedure to furnish high yields. The structures of all the synthesized compounds were confirmed on the basis of IR, H-1 and C-13 NMR, mass spectrometry, and elemental analyses data. In addition, we have also extended the scope of this strategy for obtaining 2-amino substituted benzoxazoles.